The present invention relates to a regulator circuit configured to convert a power supply voltage supplied from an input terminal and output the converted power supply voltage to an output terminal.
In recent years, the power consumption of a battery driver for an electronic appliance has tended to reduce and along with that a demand on the electronic appliance to operate in a low voltage has increased. The electronic appliance of this type includes a regulator circuit for generating an internal power supply voltage used in the internal circuit of the electronic appliance from an external power supply voltage supplied from the outside.
As a regulator circuit of this type, Patent Document 1 (Japanese Unexamined Patent Publication No. 2008-192083) discloses a regulator circuit which includes an output transistor for generating a predetermined output voltage according to an input voltage and an output voltage control means which compares a voltage in which the output voltage of the output transistor is divided with a predetermined reference voltage, controls the gate voltage of the output transistor so that the divided voltage becomes equal to the predetermined reference voltage, and sets a predetermined output voltage. Patent Document 1 uses a common-drain depression N-channel metal oxide semiconductor (NMOS) whose threshold voltage is a negative voltage as an output transistor to reduce a difference between the input and the output voltage, improving efficiency and allowing the regulator circuit to be used even if the input voltage from the outside is lowered.
Non-Patent Document 1: (Koichiro Ishibashi et al., “A Voltage Down Converter with Submicroampere Standby Current for Low-Power Static RAM's,” IEEE Journal of Solid-State Circuits, Vol. 27, No. 6, June 1992) discloses a voltage follower including a differential amplifier and a depression NMOS transistor.